1. Field of the Invention
The present invention relates to improvements in a valve lifter of a valve mechanism for an internal combustion engine.
2. Description of the Prior Art
Japanese Patent Provisional Publication No. 63-147907 discloses a typical valve lifter of a valve mechanism for an internal combustion engine. As shown in FIGS. 8A and 8B, such a valve lifter has a valve lifter body 20 which has a bottom portion 20a and a recess. 21. An inner shim 23 is embedded in the recess 21 and is in contact with a valve stem 22. The inner shim 23 is formed such that a circular plate is cut away at two opposite segment portions as shown in FIG. 8B. Accordingly, the periphery of the inner shim 23 is formed by a pair of arc portions and a pair of straight portions which are alternatively arranged as shown in FIG. 8B. Each of corners 23a of the inner shim 23 is a connecting point of the are portion and the straight portion. On the other hand, a caulking portion 25, which is of a part of a side wall defining the recess 21, is deformed so as to partly fill up the recess 21. Accordingly, projecting portions 26 of the valve lifter body 20 are engaged-with the corners 23a of the inner shim 23, respectively as shown in FIG. 8B. That is, each corner 23a is embedded in the caulking portion 25. Therefore, the inner shim 23 is fixed by the caulking portions 25 and the recess 21.
However, in the thus conventional valve lifter for a valve mechanism since the valve lifter body 20 receives a rotating force owing to the rotation of a cam 28 above the cylinder bore 27, the inner shim 23 also receives a rotating force at a portion with which the valve stem 22 is in contact. This force generates a concentration of stress at the projection portions 26 and deforms the projection portions 26 as a permanent set in fatigue. This permanent set of the projection portions 26 invites a rotation of the inner shim 23. Further, in almost all cases the valve lifter body 20 is made of aluminum alloy and the inner shim 23 is made of ferroalloy. Accordingly, due to the difference of linear expansion coefficient, the fixing between the inner shim 23 and the recess 21 is loosened to generate backlash or looseness.